Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

The invention relates to a filler material, especially for filling
cavities, especially of structural elements, to a method of production
and to a structural element. The inventive filler material comprises
particles that are coated with a reactive duroplast, whereby the reactive
duroplast is non-viscous at room temperature when not yet reacted.

Claims:

1. Filler material (3), especially for filling cavities especially in
structural elements, whereby filler material (3) comprises particles (2)
which are at least partially coated with a reactive duroplastic (1),
characterized in that reactive duroplastic (1) does not flow in the
unreacted state at ambient temperature.

2. Filler material (2) in accordance with claim 1, characterized in that
the reactive agglutinant in the unreacted state at ambient temperature
features a viscosity exceeding 1,000 Pas, preferably in excess of 2,000
Pas and more preferably in excess of 3,000 Pas.

3. Filler material (3) in accordance with claim 1, characterized in that
the thickness of the coat on particles (2) lies between 2 and 200 μm,
preferably between 5 and 100 μm, more preferably between 10 and 80
μm and most preferably at 50 μm.

4. Filler material (3) in accordance with claim 1, characterized in that
particles (2) are hollow and are preferably embodied as hollow spheres.

8. Filler material (3) in accordance with claim 1, characterized in that
the coated particles form filler material particles that feature a viscid
or a dry surface.

9. Filler material (3) in accordance with claim 1, characterized in that
the glass temperature of the non-cross-linked and pre-cross-linked
duroplastic exceeds 30.degree. C.

10. Filler material (3) in accordance with claim 1, characterized in that
the coated filler material particles are dusted with a powder which is in
particular thermoplastic powder and/or a latent hardener of the
duroplastic and/or an inert filler.

11. Process for preparing a filler material (3), in particular in
accordance with claim 1, whereby particles (2) are coated with a reactive
duroplastic (1), characterized in that coating of the particles (2) with
duroplastic (1) is effected inside a centrifugal mixer.

12. Method for preparing a filler material (3), in particular in
accordance with claim 1, whereby particles (2) are coated with a reactive
duroplastic (1), characterized in that the temperature of reactive
duroplastic (1) during the mixing process is such that the viscosity of
the duroplastic lies between 20 and 50 Pas.

13. Structural element (4) having a cavity that is filled at least
partially with a filler material (3) in accordance claim 1, whereby
filler material (3) in particular is cured.

Description:

THE TECHNICAL DOMAIN

[0001]The present invention relates to a filler material, especially for
filling cavities, in particular of structural elements, whereby said
filler material comprises particles that are coated with a reactive
duroplastic. The present invention relates furthermore to a process for
manufacturing a filler material, in particular a filler material as
proposed whose particles are coated with a reactive duroplastic. The
present invention relates furthermore to a structural element having a
cavity.

THE STATE OF THE ART

[0002]The production of both vehicles and containers requires that
load-bearing metal components be at once light and exhibit considerable
rigidity or solidity. This objective can, in many instances, be achieved
if metal components are designed to have, for example, a sandwich
construction wherein the cavities are filled with a porous material, for
example, foam materials. Such sandwich structures are produced by bonding
two metal covering layers to a foam core or by introducing foam between
such layers, for example, with the aid of a PUR Reactive Resin System.
Known in the art in addition to such synthetic material foams are the
widely-known metallic foams that have the advantage of absorbing greater
amounts of energy when undergoing deformation.

[0003]Also well known in the art is a method for obtaining reinforcing
material for filling a cavity that involves pouring hollow spheres into a
cavity which, after sealing, is filled with a low-viscosity agglutinant
following which the interstices are filled with the agglutinant, which
then hardens. The notable disadvantage of this method is that a cavity so
prepared must be tightly sealed in order to prevent the egress of
agglutinant.

[0004]Furthermore known in the art is a method in which particles of
filler material contained in a fluid layer are coated by means of
spraying with an epoxy resin system. The disadvantage attending this
method is that the viscosity of such epoxy resin systems must be weak
enough to allow application by means of spraying. At the same time,
however, the epoxy resin system must be sufficiently reactive so as to
permit it, in the environment in the fluid layer, to rapidly polymerize
when heated.

[0005]Consequently, this objective calls for a solution which, following
fluidization, involves the formation on the sphere surface of a partially
cross-linked coat that exhibits both good adhesive properties and good
mechanical load resistance. It would, however, be more expensive to
render such coating more susceptible to sintering and more reactive at
higher temperatures.

SUMMARY OF THE OBJECTIVES OF THE PRESENT INVENTION

[0006]The object of the present invention is, therefore. the preparation
of a filler material, a method for producing such filler material and a
structural element that obviates the drawbacks of the state of the art.

[0007]It is proposed that the aforementioned objective be satisfied in-a
filler material, more particularly for filling cavities especially in
structural elements, whereby such filler material comprises particles
that are coated with a reactive duroplastic which, in the unreacted
state, does not flow at ambient temperature. The aforementioned objective
will furthermore be satisfied by means of a method for the production of
a particularly novel filler material comprising particles that are coated
with a reactive duroplastic.

[0008]It is proposed firstly that the filler material be introduced into
cavities in the structural element without requiring expensive structural
modifications while obviating the egress of filler material, and secondly
that the duroplastic system, for example an epoxy resin system, need not
be weakly viscous and relatively highly reactive at the same time.

[0009]Further advantageous embodiments of the present invention will be
described in the subsidiary claims.

OVERVIEW OF THE DRAWINGS

[0010]The present invention will next be described in greater detail with
the aid of drawings. The same elements appearing in different drawings
are referenced with the same reference numerals.

[0011]Shown in FIG. 1 is a plurality of filler material particles of the
proposed filler material 3 whereby such filler material particles are
formed from particles 2 that are, more particularly, hollow-bodied
particles enveloped substantially uniformly with a duroplastic 1.

[0012]Shown in FIG. 2 is a structural element 4 featuring a cavity that is
filled with a filler material 3.

[0013]In order to better convey the essence of the present invention, only
the essential elements will be illustrated.

THE EMBODIMENT OF THE PRESENT INVENTION

[0014]The present invention relates to compounds for duroplastics 1 or
rather duroplastic materials 1 and in particular comprises epoxy resin
formulations having a latent hardener, more particularly a thermal
hardener which, preferably together with, for example, reactive fluid
elastomers, form impact-resistant modified epoxy resin systems which,
when in the unreacted state, do not flow at ambient temperature. In other
words, at ambient temperature, such systems exhibit a sufficiently high
viscosity typically in excess of 1,000 Pas, preferably in excess of 2,000
Pas and most preferably in excess of 3,000 Pas. Such formulations are
applied at higher temperatures or at ambient temperature to the hollow
spheres, i.e. to the particles 2, preferably by means of a centrifugal
mixer. This novel method, astonishingly, permits the duroplastic 1 to
homogenously or uniformly coat the particles or spheres. The viscosity
level selected determines the desired degree of viscidity of the coated
spheres. Should viscid coatings not be desired, said coatings can be
dusted with a dry powder or be partially cross-linked by means of the
addition of a second non-latent hardener immediately prior to coating.

[0015]The particles are preferably hollow, are preferably embodied as
hollow spheres and most preferably are substantially uniformly coated.
Since the insides of the particles are hollow, it is possible to produce
an especially lightweight filler material. This confers considerable
stability on the structural elements without adding an inappropriate
amount of weight thereto. If the particles are embodied as spheres,
especially as hollow spheres, their surface which is to be coated, is
comparatively small and their ability to withstand impinging forces
comparatively great.

[0016]It is furthermore proposed that the duroplastic exhibit unlimited
storage stability at ambient temperature and be impact-resistant
modified.

[0017]This arrangement permits the duroplastic material to be stored for
extended periods of time, which in turn permits the filler material, due
to relatively low logistical costs, to be produced in a cost-effective
manner. It is consequently proposed that no or very little cross-linkage
of the duroplastic material occur while the particles are being coated
with duroplastic. Most of the cross-linkage of the duroplastic can take
place during the full curing effected inside the structural element into
which the particles to be coated have been poured. Such curing process
when implemented, for example, in the automobile industry involves either
pouring the coated particles into the cavity prior to cathode immersion
painting and subsequent curing inside the baking kiln or, alternatively,
pouring into the cavity and curing inside the baking kiln following
cathode immersion painting. This method affords the further advantage of
conferring increased stability on the duroplastic material and therefore
also on the "filled" structural element.

[0018]Especially suitable as duroplastic systems are impact-resistant
modified single-component epoxy-resin systems, which, when not
crossed-linked at ambient temperature, exhibit a sufficiently high
viscosity level typically in excess of 1,000 PAS, preferably in excess of
2,000 PAS and most preferably in excess of 3,000 PAS. Such epoxy-resin
systems comprise typically mixtures of so-called solid resins or addition
compounds (i.e. diphenols or dicarbonic acids to diglycidyl ethers which
are solid at ambient temperature, and pre-elongated diglycidyl ethers of
diphenols) with fluid diglycide ethers, impact-resistance enhancers such
as thermoplastics, e.g. poly-p-phenylene oxide, polyalkylene oxide
glycidyl ether, glycide ethers or reactive liquid rubbers and filler
materials. Typical molecular weights for the solid resins or addition
compounds lie between 800 and 10,000 Dalton, preferably between 900 and
8,000 Dalton. Employed preferably as hardeners are latent hardeners such
as dicyandiamide or other substituted urea compounds that enable
cross-linking starting at 160° C. In order to achieve partial
cross-linking of the coat, it is also possible, in addition to latent
hardeners, to add conventional epoxy hardeners such as polyphenols,
mercaptans, amines, or anhydrous carbonic acids to the agglutinant
systems immediately prior to coating. It is also possible, immediately
prior to the coating procedure, to add diisocyanate to the agglutinant
system and thus achieve pre-cross-linking via the β hydroxy groups
of the epoxy addition compounds. Supplementary pre-cross-linking leads to
higher molecular weights which, in turn, leads to a higher glass
temperature and to a lowering of viscidity. Such systems are non-viscid
when the glass temperature of the uncross-linked and pre-cross-linked
viscid layer exceeds 30° C.

[0019]The coat is preferably selected to be as thin as possible,
especially in light structure applications. The weight of the agglutinant
as a proportion of that of the sphere lies between5% and 80%, preferably
between 20% and 50% and most preferably 30%. The thickness of the coat
lies between 2 and 200 μm, preferably between 5 and 100 μm, more
preferably between 10 and 80 μm, and most preferably 50 μm.

[0020]It is furthermore contemplated by the invention that the coated
particles will form filler material particles that feature either a
viscid or a dry surface. The viscosity of the coated spheres or coated
particles can be selected to provide a desired degree of viscidity, an
arrangement, which, owing to adhesion to the inner walls, is of
particular advantage where cavities of structural elements are to be
filled. It is, however, also contemplated by the present invention that
the coated particles not be viscid when used in other applications. In
such applications, it is proposed that it be possible to sprinkle the
coat with a dry powder which is employed to render the coat non-viscid or
non-adherent.

[0021]It is furthermore proposed that the filler material particles be
dusted with a powder, which is in particular. a thermoplastic powder
and/or a latent hardener of the duroplastic and/or an inert filler. Use
of thermoplastic powder such as poly(vinyl butyral) powder and/or
polyamide powder, advantageously facilitates impact resistance. In
addition to the thermoplastic powders, it is possible to use pulverized
minerals or fillers such as, for example, calcium carbonate,
wollastonite, quartz powder or pyrogenic silicic acid. Such powder can
also feature, alone or in combination with other substances, a
micronized, solid and latent hardener, such as, for example, dicyanamide.
In this configuration of the present invention, it is advantageous to add
part of the hardener as part of the duroplastic formulation and to add
the rest of the hardener by sprinkling it in powder form. It is
furthermore proposed that the powder employed for dusting alone or in
combination with one or more other substances be an organic or a mineral
filler.

[0022]In accordance with the present invention, it is preferable that the
particles be coated with the duroplastic inside a centrifugal mixer. In
such centrifugal mixer, an arm rotates at high speed in one direction in
concert with a basket which, being attached to such arm, rotates in the
opposite direction (hence the expression "Dual Asymmetrical Centrifuge")
so as to permit the material inside the machine to be thoroughly and
rapidly mixed together, even when the viscosity of the duroplastic
material, for example, is relatively high, and in particular exceeds a
value at which spraying of the material would otherwise be enabled. The
viscosity level can be modified by adjusting the temperature, to which
end the agglutinant system is warmed until a viscosity of between 20 and
50 Pas is reached.

[0023]Four embodiment examples will be described in greater detail
hereunder:

EXAMPLE 1

Coated Spheres, Viscid Surfaces, Resin System (SikaPower ®9496/3).

[0024]In this case, hollow steel spheres 3.2 mm in diameter, were used at
a packed density of 0.36 g/ml. Employed as the duroplastic 1 for the
coating material was a commercially-available structural agglutinant
(SikaPower ®0496/3). Assuming homogenous coating of the spheres, it
was anticipated that the coat enveloping the spheres would have the
following thicknesses:

[0025]Both spheres and agglutinant (total mass 70 g) were transferred into
a beaker and heated to 80° C. Coating took place inside a
Speedmixer DAC 150 FV (centrifugal mixer manufactured by Hauschild). This
yielded homogenously-coated, slightly viscid, readily transportable
spheres. The slightly viscid spheres were then poured into a cylindrical
mould that had been treated with a separating agent (substituting for a
cavity inside a structural element) and allowed to cure for 30 min. at
180° C. A rigid cylinder was hereby obtained.

[0026]Individual cured spheres were then cut open and the thicknesses of
the layers measured at 200×magnification. The coat proved to be
homogenous and corresponded to the calculated layer thicknesses.

[0027]Duroplastic or agglutinant and process method as in Example 1. The
example involving 30% by weight agglutinant (70 g total weight) was
repeated. Immediately following coating, the spheres were dusted with 5 g
polyvinylbutyral Movital 60 HH. This yielded pourable spheres, which were
then transferred into a cylindrical mould, whereby after curing for 30
min. at 180° C., a rigid cylinder was obtained.

[0032]Obtained following addition of the aforementioned duroplastic to the
particles or spheres, were filler material particles which, in the
uncured state, exhibit a weakly-viscid surface. This was accomplished by
mixing hollow bodies or particles, in particular hollow steel spheres, as
described in Examples 1 and 2, with the duroplastic inside the
centrifugal mixer, whereby such particles became coated with the
duroplastic.